Diels-Alder reaction products between decatriene and maleic anhydride (hereinafter referred to as "maleinized decatriene") such as a reaction product between maleic anhydride and allo-ocimene (hereinafter referred to as "maleinized allo-ocimeme") and a reaction product between maleic anhydride and myrcene (hereinafter referred to as "maleinized myrcene") can be used as hardeners for epoxy resins and as acid components for preparing unsaturated alkyd resin. However, many of these maleinized decatrienes are in a solid state at room temperatures and, from the point of view of reactivity and workability, it is desirable to liquefy them for the application to the above-described uses. Thus, liquefaction of the solid maleinized decatriene is necessary.
As the conventional process for liquefying maleinized allo-ocimene, B.P No. 906,017, for example, describes to liquefy maleinized allo-ocimene by heat-treating at temperatures of from 190.degree. to 240.degree. C. for a long time to cause thermal isomerization. However, such process of isomerization by heat-treating for a long time involves thermal decomposition even when conducted in a nitrogen stream, and hence it has the defect that liquefied, maleinized allo-ocimene is obtained only in a low yield after purification by distillation. And, the liquefied product obtained by the distillation purification often forms crystals 2 to 3 days after the preparation though it is temporarily liquid upon preparation and, even when it is in a liquid state at normal temperatures, it crystallizes at low temperatures of about 0.degree. to 10.degree. C. This specification describes, in Example 6, that maleinized allo-ocimene heat-treated at 210.degree. to 220.degree. C. for 14 hours crystallizes when allowed to stand, and that additional heat treatment for 5 hours at 210.degree. to 220.degree. C. provides a liquid product which does not crystallize even when allowed to stand at normal temperatures. However, such process capable of liquefying maleinized allo-ocimene only through long-time heat treatment is seriously disadvantageous from the point of industrial practice.
U.S. Pat. No. 3,078,235 describes a liquid epoxy resin hardener prepared by blending maleinized allo-ocimene, maleinized myrcene, and hexahydrophthalic anhydride. However, blending of the normally solid materials to liquefy them requires a melt-mixing step, thus leading to high cost.
The present invention provides a process for liquefying normally solid maleinized decatriene with ease and with industrial advantages.